Emo is a genre of rock music which appears to fall somewhere between Goth and grunge on the post-punk rock spectrum. Although there is a significant amount of disagreement on this subject, the term is said to be short for "emotive punk", a successor to straight-edge punk rock originating in the late 1980s. Other sources say that it's short for "emocore," an emotionally charged form of softcore punk which started in the Washington, DC area during the mid-1980s. Emo music is definitely derived from the anarchic punk sound, but is often described as the flipside of the grunge sound originating in Seattle.
To understand emo, it might help to start from the beginning. First there was hardcore punk, an anarchic and energetic form of music that provided an alternative to disco and heavily produced pop music of the early 1980s. By the mid-1980s, however, many of the hardcore punk bands had disbanded or changed directions musically. This left a very large hole for local hardcore or alternative bands to fill. Some bands developed an edgier style of playing the same three power chords as original punk, but with the addition of philosophical or angst-ridden lyrics sung in a more emotional style than straight punk rock. This became known as emotive punk.
While emo worked its way from the Washington, DC area westward, other groups in Seattle were exploring essentially the same musical territory. These bands became popular in the San Francisco Bay area about the same time that grunge rock bands took over the Seattle music scene. While grunge rock performers and fans adopted a scruffy, unwashed image, emo performers and their fans often wore heavy eye makeup, dyed their hair jet black and adopted a more metrosexual look. Eventually, the genres became uncomfortably linked together in record stores and music industry publications.
While grunge enjoyed a brief but memorable period of time on the pop charts, emo bands tried very hard to remain non-commercial. This aversion to all things commercial is a hallmark of the emo music scene. The albums are often recorded on cheap vinyl LPs using vintage or secondhand recording equipment. Emo musicians use tube-based amplifiers and inexpensive guitars, not solid state amps or tricked-out modern electric guitars. Performers have been known to stage extended jam sessions ending with real emotional outbursts, such as sobbing or primal screaming onstage. Fans of the genre appreciate the honesty and rawness of the bands' emotional performances.
There have been a handful of emo bands which have found commercial success, such as Jimmy Eat World, Fall Out Boy or Dashboard Confessional, but a number fans consider these bands to be corporate versions of the emo music scene. Many of the most influential bands never made it out of their small hometowns, and the lifespan of an average group is rarely more than two or three years. The emo musical scene sees itself as a rightful heir to the hardcore punk legacy, even though many bands incorporate a few guitar arpeggios and sensitive lyrics to the straightforward, high-speed chord crunches of the original punk genre.